Researchers have found a way to breach the body's natural defences and
deliver genes and drugs into the brain.

The method shows promise for treating a host of brain disorders such
as Parkinson's disease.

The brain is protected by a membrane formed by tight connections between
the cells that line the blood vessels that supply it.

This is known as the blood-brain barrier, and is designed to ensure
that the brain is immune from attack from foreign substances circulating
in the blood stream.

Only a few molecules that are recognised by the cell receptors are allowed
to pass through.

However, it also means that it has proved virtually impossible to deliver
genes or drugs into the brain, unless they are injected directly into its
tissue.

Even this is flawed, because it is difficult to ensure an even distribution
throughout the brain's tissue.

New Scientist magazine reports that a team from the University of California,
Los Angeles has come up with a way to solve the problem.

So far their research has only been tested on primates - but the same
principle should apply for humans.

The US team has been able to smuggle genes past the brain's defences
by hiding them inside fatty spheres called liposomes.

These liposomes are coated with a polymer which is impregnated with
antibodies similar to those produced by the immune system to fight disease.

The presence of these antibodies effectively tricks the cell receptors
into letting the liposomes pass, where they can deliver their cargo to
brain cells.

Good results

The US team initially tested the technique in rats, but found that it
produced even better results in rhesus monkeys.

Dr Savio Woo, director of gene therapy at the Mount Sinai School of
Medicine in New York, told New Scientist: "To reach the central nervous
system through the blood-brain barrier in a non-human primate with this
kind of efficiency - that's absolutely fantastic."

The liposomes do not appear to have any toxic side effects.

They do deliver genes to other organs besides the brain, but scientists
are able to switch gene activity on and off so that they are active only
in the desired tissues.

The technique has already showed promise as a possible treatment for
Parkinson's disease.

In lab tests, rats with Parkinson's symptoms showed substantial improvement
after they were injected with liposomes containing a gene that boosts production
of a crucial enzyme.

Separate tests on mice have shown that the liposomes can also deliver
treatment which can block the development of brain tumours.

Dr Russell Lonser, of the US National Institute of Neurological Disorders
and Stroke who has also carried out research into how to cross the blood-brain
barrier, told BBC News Online the latest study was promising.

He said: "It may have several exciting potential uses, but additional
studies and questions must be answered to determine the precise clinical
applications of this technology."

Robert Meadowcroft, Director of Information, Policy and Research at
the Parkinson's Disease Society said: "This research appears to offer a
major step forward in terms of our understanding of how we can transport
genes to the affected parts of the brain.

"However, the Parkinson's Disease Society remains cautious of the effectiveness
of gene therapy's affect on the overall progression of the disease itself,
until findings of large scale clinical trials are published."